The present invention relates to air-conditioning systems for motor vehicles. More particularly, the invention relates to a motor vehicle air-conditioning system having a compressor driven by the motor vehicle engine through a clutch which is disengaged during the periods of acceleration of the vehicle.
Conventional air-conditioning systems, often provided in motor vehicle for cooling the vehicle passenger compartment, comprise a refrigerant circulation system having a compressor, an evaporator and a condenser. The compressor is driven directly by the vehicle engine. Because of the high power requirements of the compressor, the engine output available for propulsion is often noticeably reduced. Especially in vehicles with small engines, the accelerating ability of the vehicle is therefore diminished, particularly at the lower engine speeds: an effect which sometimes leads to difficulties in traffic. To overcome this disadvantage, it is known to couple the compressor to the engine via a clutch which is automatically disengaged during periods of acceleration of the vehicle.* FNT *The terms "acceleration" and "accelerating", as used throughout this specification, are intended to include all instances in which maximum available engine output is called for. For example, this term is intended to include the situation in which the vehicle is "lugging" uphill at wide-open-throttle but is not actually increasing in speed.
The U.S. Pat. No. 3,462,964, discloses a particular air-conditioning system of this type in which the compressor is disconnected from the engine by means of a control mechanism acting on the compressor clutch and governed by the vacuum present in the intake manifold of the engine. During acceleration of the vehicle, when the vaccum is reduced to a selected minimum value, the control mechanism is activated. This prior art arrangement has the disadvantage that, depending upon the vacuum conditions of the engine, the compressor of the air-conditioner may sometimes remain shut off for a considerable period of time.
An object of the present invention is to provide an air-conditioning system of the type described above which is designed to avoid any prolonged disconnection of the compressor.